<DataField Id="content" IsArray="FALSE">
<DataType>
<ExternalReference location="byte&lt;&gt;"/>
</DataType>
</DataField>
contentType : with Basic type->String
And set the actual parameters for var_attachments to the String "content",
and for var_attachments_mime_types set to the String "contentType":
<ActualParameter>"restresult_content"</ActualParameter>
<ActualParameter>"restresult_contentType"</ActualParameter>
The log file says: